Change packt img

doc/dhcp_server/port_based_dhcp_server_high_level_design.md

@@ -82,32 +82,27 @@ Configuration of DHCP server feature can be done via:
 * SONiC CLI
 
 # 2 Functionality
-DHCP server listens to port 68 and waits for messages from client. DHCP server and DHCP client complete IP address assignment through four-step packet interaction:
-1. Discover
+DHCP server listens to port 68 and waits for messages from client. Below are three common scenarios:
 
-  DHCP client requesting DHCP IP for the first time does not know the IP address of DHCP server, and sends a DHCP DISCOVER packet in broadcast mode.
+**1) Establish new lease**
 
-2. Offer
-
-  DHCP server performs matching after receiving the DHCP DISCOVER packet, selects an available IP address for allocation according to the configuration, and sends a DHCP OFFER packet.
-
-3. Request
+<div align="center"> <img src=images/dhcp_process.png width = 520 /> </div>
 
-  After DHCP client receives the OFFER packet, it sends a DHCP REQUEST packet in the form of broadcast, which contains information such as the DHCP server identifier and client address selected by the client.
+**2) Renew old lease**
 
-4. Acknowledge
+<div align="center"> <img src=images/dhcp_process_renew.png width = 520 /> </div>
 
-  After receiving the REQUEST packet from the client, the DHCP server responds with a DHCP ACK, indicating that the IP address requested in the REQUEST packet has been allocated successfully.
+**3) Release old lease**
 
-<div align="center"> <img src=images/dhcp_process.png width = 520 /> </div>
+<div align="center"> <img src=images/dhcp_process_release.png width = 520 /> </div>
 
 # 3 Design
 ## 3.1 Design Overview
 The design overview at a high level is as below. The details are explained in the following subsections.
 - Configuration tables for the DHCP server entries.
+- State tables for the DHCP server counter and lease entries.
 - Design is centered around the dnsmasq insides dhcp_relay container.
 - Configuration file for dnsmasq is generated by related configuration tables.
-- State tables for the DHCP server counter and lease entries.
 
 ## 3.2 DB Changes
 ### 3.2.1 Config DB
@@ -394,8 +389,6 @@ Below sequence figure describes the work flow how dnsmasq updates lease table wh
 <div align="center"> <img src=images/lease_update_flow_release.png width=400 /> </div>
 
 ### 3.6.4 Count Table Update Flow
-This sequence figure describe the update work flow for updating packet counter table in STATE_DB.
-
 Below sequence figure describes the work flow about server logging process while sending or receiving DHCP packets.
 <div align="center"> <img src=images/packet_log_flow.png width=400 /> </div>